6066 (1960-1966) GMC Truck Club

I've followed the no lead and fuel additive controversy since no lead gas first was announced. Used to be monthly articles by technical people like CJ Baker or Gordon Jennings in Hot Rod Magazine or Cycle magazine that could explain the difference between detonation and preignition, or how octane actually worked to prevent your engine from detonating. Or how oil or grease was the best lubricant for specific purposes. From what I've read, very little tetra ethyl lead is needed to protect exhaust valves and valve seats. The V-6's are rather low compression engines, what gets them in trouble is the duty cycle they were built to endure. If you don't drive your GMC much, I'd fill it with straight gasoline, no ethanol, ethanol is hydroscopic, attracts water which causes storage problems. Then add a couple gallons of leaded race gas, Unocal, Sunoco, VPN, even low lead 100 octane aviation gas. For most light duty these trucks see anymore the blend of leaded gas and a good non ethanol gas is the best you can feed them. They should run like it's 1965 all over again. I'd suggest 15-20% race gas is enough. I find it is about $2- $2.50/gallon more than straight gas.

Back when I was running gasoline farm tractors wide open, pulling as hard as they could 8-10-12 hours a day the inside of the exhaust would be a medium gray, if you were letting them loaf they would be coal black. Excellent indicator of your combustion chamber temp. With the mixed gas they will have a nice medium gray color inside the tailpipe after an hour at 65 mph.